HP Series 37 Reference Manual page 99

Test Descriptions
SEP 84
3-6
the Perform I/O is done without flush, the Receive Buffer may begin with some data from the
previous operation. The last step is to try to find individual ports that have not interrupted in
a long period of time. This is done by maintaining a timer for each port. The timers for all
ports are decremented each time any port interrupts. If the timer for a port reaches zero, an
error is reported on that port.